How can I make the propeller to rotate?
He pressed "G" to grab and then just clicked the mouse.  What that did is give Blender a detectable action.  In other words, if your grabbing then you're probably moving something, so Blender will automatically insert a keyframe at the current frame.  It's a little hacky.  

A better (and more deliberate) way to do this, in my opinion, is to press i whenever you want to insert a keyframe.  Just select the action that you want to keyframe.  i works on almost everything, even things like shader nodes.  Using this method prevents you from keyframing things you never intended.



EDIT: There are whole videos and articles dedicated to keyframing.  But I'll add this: by default, Blender will "curve" the value.  In other words, say for instance a car... going from rest to full speed takes time.  In the same way, Blender automatically accelerates to the desired "speed" or value and then decelerates at the end.  

You can change the interpolation to be linear in the Graph Editor: